EUGLENA, AMOEBA, AND PARAMECIUM 285 



Behavior 



Euglena usually lives near the surface of the water if the light 

 there is not too intense, and when in the active phase swims about. 

 This animal displays positive phototropism and is easily stimulated 

 by changes in intensity of light. If the light is too intense, there 

 will be a negative response. A medium light is optimum for it. 

 There is naturally an attraction to light in those forms which utilize 

 it in the manufacture of food by photosynthesis. Direct, intense 

 sunlight, however, is injurious to them. When Euglena swims 

 through the water, its anterior end with the flagellum goes foremost 

 and is first to reach any injurious or distasteful environment. When 

 it encounters such a condition in the medium, it stops and turns 

 sharply in another direction and attempts to move out of danger. 

 This is known as the avoiding reaction. In these and other reactions 

 this cell exhibits the irritability that is characteristic of all protoplasm. 



Locomotion and Flagellar Movement 



Contractions and expansions take place in Euglenae when they 

 are not actively moving about. These movements resemble waves of 

 contraction (peristaltic contraction) passing over the cell. Some of 

 the larger species move about in a crawling fashion by taking advan- 

 tage of this movement. This activity is known as Euglenoid move- 

 ment. The chief method of locomotion is swimming by means of the 

 whiplike movements of the flagellum through the water. A spiral 

 path is followed due to the continuous turning of the body. The 

 flagellum is made up of an elastic outer sheath which encloses an 

 axial filament composed of one or more contractile fibrils. 



AMOEBA, OF CLASS SARCODINA 



It is likely that no microscopic organism has attracted so much 

 attention and popular interest as Amoeba. Amoeba is recognized 

 by the public generally as a simple and low form of life. Even the 

 writers of fiction speak of the range of the span of complexity of 

 animal life as extending ''from Amoeba to Man." The pedigree of 

 Amoeba is probably as long as that as of any of the animals we know 

 and involves hundreds of times as many generations as many of 

 the common animals; yet Amoeba remains in a relatively primitive 

 and simple state. Little or nothing is known about the real an- 

 cestry of Amoeba. There are many kinds or species of Amoeba, 



